Electromagnetic piano



United States Patent Inventor Elden G. Chapman Woodside, CaliforniaAppl. No. 687,246 Filed Dec. 1, I967 Patented Sept. 29, 1970 AssigneeElectric Piano Inc.

, Washougal, Washington a corporation of Washington ELECTROMAGNETICPIANO 2 Claims, 13 Drawing Figs.

U.S.Cl 84/I.I5, 84/1.17, 84/124 Int. Cl 61% 3/00, GlOh 3/06,G10h 1/02Field of Search 84/ 1 .01

[56] References Cited UNITED STATES PATENTS 1,603,920 10/ I 926 OMalley84/264X 2,263,973 11/1941 O'Brien 84/1 .15 2,486,338 10/1949 Sperry eta1 84/184 2,683,388 7/1954 Keller 84/1 .15 2,973,680 3/1961 Nolder eta1. 84/114 3,236,930 2/1966 Fender 84/ 1 .15

Primary Examiner-Herman Karl Saalbach Assistant ExaminerT. VezeauAttorney- Flehr. Hohbach, Test, Albritton and Herbert ABSTRACT: A pianohaving a conventional hammer and damper for striking the strings.Electromagnetic means coupled to the strings for converting theoscillations of the string into electrical oscillations or signals whichare electrically processed and applied to speakers to produce sound.

Patented Sept. 29, 1970 Sheet 1 of 5 BASS CONSOLE INVENTOR. ELDEN e.CHAPMAN BY 1%, M W

m v M ATTORNEYS Patented Sept. 29, 1970 Sheet 8 6 4 m 3 4 6 3 M 8 3 I 4M u 3 r,

a 8 flfl f 3 6 F, m. 7 n 4 P m I a an f\ a! z/ I P I, 4 a I 7 I I n 9 74/ 3 3 4 6p O I' 7 4 7 3 INVENTOR. ELDEN G. CHAPMAN ATTORNEYS PatentedSept. 29, 1970 3,530,756

Sheet of 5 I NVENTOR.

ELDEN e. CHAPMAN BY 1 W014i; mm W ATTORNEYS Patented Sept. 29, 1970Sheet 4 [59 5 I LLLLL LI I INVENTOR. ELDEN G. CHAPMAN BY %M, W, (WW1; W

ATTORNEYS Patented Sept. 29, 1970 Sheet INVENTOR ELDEN G. CHAPMAN BY14%,

ATTORNEYS ELECTROMAGNETIC PIANO This invention relates, in general, to anew and improved piano utilizing a combination of novel mechanical,magnetic and electronic concepts and in particular to an electronicpiano in which the vibratory motions of the strings serve to generateelectrical signals or oscillations having corresponding frequenciessuitable for processing and transformation into sound.

When electrical oscillations of audible frequency are transformed intomechanical oscillations by a loudspeaker, audible sound is produced. Ifthese electrical oscillations are under the control of the musicianfrequency by frequency (note by note), it may be said that a new type ofmusical instrument has been created. Prior art instruments of thischaracter are of two general types: those which generate their ownoscillations, and those which amplify the natural vibrations of wellknown musical instruments.

A conventional piano produces its characteristic tones by means of anaction consisting primarily of mechanical levers which serve to cause afelt hammer to move and strike one or more taut steel wires or stringsto set the same into vibration. The velocity and force of the hammer isunder control of the player or performer. A skilled performer can exertan extremely high order of control over the amplitude and other tonalcharacteristics of the sound. The wide range of amplitude results mainlyfrom the construction of mechanical linkage between the key which isstruck by the performer and the felt hammer.

Certain prior art devices have tried, without success, to do away withthe steel strings used in the conventional piano and to substitutepurely electronic means for generating the electrical tonal frequenciesor oscillations. Because of the varying parameters of the piano, such asthe decay characteristics, damping, sostenuto and softness, such priorart electronic pianos required complex electronic circuits for each noteof the scale to provide all of the above mentioned characteristics.Because of the complexity of the piano and the tones produced thereby,such prior art devices have not been entirely successful in theirimitation of string vibrations.

A second technique for amplifying the natural vibrations of well knownstringed musical instruments has resulted in the modification of thestringed instruments into quasi-electrical instruments by addition ofelectrical pickups to some part of the normal sound producing mechanism.In the case of such instruments as the banjo, mandolin, guitar andviolin, the pickup is ordinarily attached to the body of the instrument.The output of the pickup is electronically amplified and converted intosound by a loudspeaker. Such techniques are practical for small andrelatively inexpensive instruments.

In a conventional piano, when the strings vibrate, they transmitpressure differences to a bridge attached to a sound board. The largearea of the sound board is set into motion and this, in turn, agitatesthe air in its immediate vicinity to produce sound. The board isextremely elastic and is capable of reproducing the most complicatedwaveforms with minimum loss of energy. In addition, the sound board maybe made of a material of low density and of uniform texture. As isapparent from the above requirements, the production of a suitable soundboard is extremely complicated and expensive and is a key feature whichsets off the finer pianos from the less expensive ones. It is obvious,therefore, that those techniques which retain the normal tone producingmechanism are unsuitable for the electrification of a piano because thesound board would still be required and the tonal characteristics wouldagain be dependent upon its construction and quality.

It is an object of the present invention to provide a new and improvedelectromagnetic piano.

It is another object of the present invention to provide a new andimproved electromagnetic piano in which the vibrations of the stringsare converted into electric oscillations having correspondingfrequencies.

It is another object of the present invention to provide an improvedharp and frame for an electromagnetic strung piano.

The present invention overcomes the above drawbacks by providing astrung electromagnetic piano which retains the normal mechanicallinkages between the keys and felt hammers. An electromagnetic pickupconverts the mechanical oscillations of the strings into electricaloutput signals having a frequency which corresponds to the mode ofvibration of the strings which are struck. In particular, the presentinvention contemplates the use of an electromagnetic pickup in which thesteel string itself varies the reluctance of a magnetic path coupled toa coil to induce a change in current through the coil which isproportional to the change in flux. The frequency of the changes isdirectly dependent upon the mode of vibration of the string, and thestrength of the signal is dependent upon the amplitude of vibration.

The foregoing and other objects of the invention will become moreclearly apparent from the following detailed description taken inconjunction with the accompanying drawings.

Referring to the drawings:

FIG. l-is a perspective view of a piano in accordance with the presentinvention;

FIG. 2 is a block diagram of the electronic circuits associated with thepiano of the present invention;

FIG. 3 is a plan view showing a strung frame and harp constructed inaccordance with another feature of the present invention;

FIG. 4 illustrates a pedal mechanism suitable for use in the presentinvention;

FIG. 5 illustrates in cross-section the piano action and theelectromagnetic pickups of the present invention;

FIG. 6 is a sectional view taken along the line 6-6 of FIG. 3 showingthe pinblock support;

FIG. 7 is a sectional view taken along the line 7-7 of FIG. 3 showingthe pinblock support;

FIG. 8 is a plan view of the electromagnetic pickup shown in FIG. 3;

FIG. 9 is a sectional view taken along the line 9-9 of FIG. 8;

FIG. 10 is an enlarged sectional view showing the magnetic flux paththrough the pickup and associated strings;

FIG. 11 is a suitable voicing circuit associated with theelectromagnetic pickup;

FIG. 12 is a plan view showing another strung frame and harp; and

FIG. 13 is a perspective view of another electromagnetic pickup.

A console piano 10 is illustrated in FIG. 1. The piano includes akeyboard 11. The full keyboard may include 88 keys. whereas a smallerand more portable piano may include 64 keys. As will be presentlydescribed, the keys 11 are associated with a conventional lever andhammer action for striking the strings.

The keyboard 11 is suitably supported from the cabinet 12 which servesto enclose the frame and harp to be presently described. The electricalcomponents which serve to generate and process the electrical signalsare mounted within the cabinet. The electrical components includeelectromagnetic transducers and amplifiers. One or more speakers 13 areindicated in dotted line behind grill l4 and serve to convert theelectrical signals into sound.

Since the tones of the piano are produced through an electromagneticsystem, the bass, treble and volume can be electrically controlled. Forthis purpose, controls 20 are provided. These controls are designated B,T and V for bass, treble and volume, respectively. Additional tonaleffects such as vibrato and tremolos and the addition of variousharmonics to the fundamental notes to imitate the quality of the toneissuing from other stringed instruments such as a harpsichord,rink-a-tink piano and guitar can be easily introduced, and such areindicated in the electrical circuit of FIG. 2.

Referring more specifically to FIG. 2, there is illustrated anelectromagnetic pickup 21, to be described in detail. Theelectromagnetic pickup includes bass, midrange and treble outputs 22, 23and 24 connected to a voicing circuit 26. The voicing circuit varies therelative amplitude of the output and combines and applies the voicedoutput to a preamplifier 27. The output from the preamplifier isamplified by amplifier 28 and applied to a speaker 29. The preamplifier27 and amplifier 28 may be of conventional construction such as used inhigh fidelity'equipment and may include such controls as volume, bassand treble. A shaper 31 may also be connected in the preamplifier. Theshaper serves to shape the signals at the preamplifier to achieve thevarious special tonal effects described above. The shaper may be ofconventional design. As shown, it includes a harp control B, aharpsichord control I-IC, rink-a-tink control RT, and tremolo control T.The power amplifier 28 may include a volume control 32 which iscontrolled by a pedal for pedal control of the volume knob V, on theconsole.

Referring now more particularly to FIG. 3, there is shown a harp andframe in accordance with the present invention. As previously described,the harp arrangement for a conventional piano includes a harp made ofaluminum or cast iron on which the strings are mounted to cooperate witha bridge which activates or drives the sounding board.

In the present invention there is provided a tubular rectangular steelframe 36. A cross member 37 is spaced from the top of the frame todefine a pinblock space. Spaced vertical reinforcing members 38 areprovided between the bottom of the frame 36 and the cross member 37.Channel members 40 are secured to the frame and cross member to receiveand hold the wooden pinblock 39. This is more clearly illustrated inFIGS. 6 and 7. Tuning pins 41 are inserted in the pinblock in aconventional manner.

A member 42 extends diagonally across the frame and is secured theretoand to the reinforcing members 38. The member 42 serves to receive hitchpins 43.

The strings are strung between the tuning pins and the hitch pins. Anumber of the strings are so-called bi-strings while 12 of lowerfrequencies are singles. These two types of strings are designatedgenerally by the arrows 44 and 46, respectively, on FIG. 3. A top railor bridge 47 is interposed between the pinblock and the strings and abottom rail or bridge 48 is interposed between the diagonal member andthe strings. In contrast to a conventional piano in which the bottomrail is mounted to the sounding board, the bottom rail in thisparticular instance is mounted directly on the member 42.

It is particularly noted that in the present design all the strings areparallel to one another and arranged vertically simplifying thestringing. The piano is tuned in a conventional manner by adjusting thetuning pins. It is to be noted that the frame and harp is a single unitmade of one material and that because of its unitary construction, it isless sensitive to environmental changes than a conventional piano.

An electromagnetic pickup unit 51 is coupled to the strings. The unit isdisposed generally parallel to the member 42 between the top and bottombridges. The unit is shown in more detail in FIGS. 8-10. It comprises atray or housing 52 made of high permeability magnetic material. The tray52 is in the form of an open box. The lower portion of the box hasoutwardly extending tabs 53 provided with openings 54 for mounting theelectromagnetic pickup unit in coupled relationship with the strings.One side wall of the box is provided with a plurality of lips or tabs 56which extend outwardly substantially parallel to the upper surface ofthe box. The unit includes coils 57, 58 and 59 wound about a permanentmagnet bar 61 in the manner shown. Thus, the permanent magnet bar isdisposed longitudinally within the box 52 and the coils 57, 58 and 59are wound thereabout and disposed between the magnet and the adjacentsides of the box. Epoxy or other suitable material may be introduced toform a sealed unit. It will thus be seen that the magnetic lines willextend upwardly from the magnet as shown from the north pole, across thegap between the magnet and the side walls of the tray and then travelalong the low reluctance path back to the south pole of the magnet. Whenthe pickup is placed adjacent to a vibrating string, a portion of themagnetic path will be through the lower reluctance string. For purposesof illustration, FIG. 10 shows a single string in cooperation with theupper surface of the electromagnetic pickup unit. The string 60 isdisposed a distance 62 above the upper edge of the box. The magneticlines will then travel upward from the magnet as shown by the arrow 63along the string and back down to the tray or box 52 as shown by arrow64. It is readily apparent that as the string vibrates, the distancebetween the string and the edges of the tray is varied thereby varyingthe reluctance path. Since the electromotive force is constant, theamount of flux will vary. This change in flux induces an electriccurrent in the portions of the coil associated therewith. Referringparticularly to the lip 56a associated with the string, it is seen thatthe return path for the flux extends along the entire lip. Thus, bybending the lip upwardly towards or away from the string, the reluctancecan be incrementally varied. This feature is used to voice" the piano.

The electromagnetic pickup is mounted in the cabinet closely adjacent tothe strings whereby the vibratory motion of the string will result in achange in the flux linkage on the coils. In practice, it has been foundthat the spacing of about oneeighth inch from the strings produces asuitable output signal. Each of the strings will induce its own currentsand there will be a mixing action on the coil to provide a complexoutput signal for each of the bass, midrange and treble windings.

The complex signals on lines 22, 23 and 24 are applied to voicingcircuit 26. A suitable circuit is shown in FIG. 11 and includes threeresistive-capacitive circuits having a common output. Each of thecircuits includes two serially connected potentiometers 66 and 67coupled by a capacitor 68. The potentiometers provide for varying thegain or amplitude which the capacitor provides in connection with theassociated resistance of a frequency sensitive delay circuit.

Referring to FIG. 5, there is shown a conventional piano action and, assuch, will only be briefly described. The action shown includes a key 71mounted on pins 72 and guided for rocking movement by the forward pins73. Depression of the front end of the key as shown at the arrow 74serves to lift the rear of the key and lift the rod 76 which rotates thelever 77. This rotates lever 78 which causes spoon 79 to strike thelever 81 which lifts the associated damper 82 away from the string.Further rotation of the lever 77 causes the member 83 to strike thestriker 84 which then drives the felt hammer 86 in the direction ofarrow 87 to strike the associated string.

The tone is modified by means of two pedals, the left-hand pedal movingthe hammer nearer to the strings and, therefore, decreasing the force ofthe blow. The right-hand pedal lifts all of the dampers simultaneouslyfrom the strings so as to sustain harmony as long as required and notmerely to increase power. In addition, a central pedal is often added,called a sustenuto which, instead of lifting all the dampers, affectsonly those which happen to be already lifted keeping them so lifteduntil the pedal is released. Thus, one is able to sustain a chordleaving the otherhand free for other notes. Since, however, the volumeof the tone of the present invention can be electronically controlled,the left-hand pedal 91, where the usual soft pedal is placed, is used asa volume pedal.

The pedal action is more clearly shown in FIG. 4 and includes theconventional pedal 92 pivoted at 93 and extending through aspring-loaded plunger 94. The other end of the spring-loaded plungermay, for example, rotate a gear 96 which, in turn, drives gear 97attached to a potentiometer connected in an amplifier circuit to controlthe volume. This is indicated generally in FIG. 2 by the line markedpedal". The level of volume can also be adjusted at the console toprovide maximum full amplification for the audio level of the room whichcan then be varied by the foot pedal as desired during playing of anumber.

Referring now more particularly to F [G 12, there is shown anotherembodiment of a harp and frame in accordance with the present invention.

The frame 101 is made of tubular metal such as tubular steel. Crossmember 102 is spaced from the top of the frame to provide a space forthe pinblock. Reinforcing members 103 are provided between the bottom ofthe main frame and the cross member 102. Tuning pins 107 are inserted inthe pinblock in a conventional manner. A curved member 108 extendsacross the frame and serves to receive hitch pins 109. The strings arestrung between the tuning pins and the hitch pins. A number of thestrings are so-called bi-stn'ngs while [-2 of lower frequencies aresingles. These two types o fstrings are designated generally by thearrows 111 and 112, respectively, on FIG. 12. A top rail or bridge 113is interposed between the pinblock and the strings and a bottom rail orbridge 114 is interposed between the curved member and the strings.Again, it is particularly noted that in the present design all thestrings are parallel to one another and arranged vertically simplifyingthe stringing.

It is to be noted that the frame and harp is a single unit made of onematerial and that because of its unitary construction, it is lesssensitive to environmental changes than a conventional piano. Aplurality of electromagnetic pickup units 116-120 are coupled to thestrings. The units are disposed generally one-third of the distancebetween the bottom and top bridges.

One pickup unit is shown in more detail in FIG. 13. It comprises a trayor housing 122 made of high permeability magnetic material. The tray 122is in the form of an open box. The lower portion of the tray hasoutwardly extending tabs 123 provided with openings 124 for mounting theelectromagnetic unit in the cabinet adjacent the strings. One side wallof the box is provided with a plurality of lips or tabs 126 which extendoutwardly substantially parallel to the upper surface of the box. Theunit includes a coil 127 which is wound about a permanent magnet bar 128in the manner shown. Thus, the permanent magnet bar is disposedlongitudinally within the box 122 and the coil 127 is wound thereaboutand disposed between the magnet and the adjacent sides of the box. Epoxyor other suitable material may be introduced to form a sealed unit. itwill thus be seen that the magnetic lines will extend upwardly from themagnet as shown from the north pole, across the gap between the magnetand the side walls of the tray and then travel along the low reluctancepath back to the south pole of the magnet. When the pickup is placedadjacent to a vibrating string, a portion of the magnetic path will bethrough the lower reluctance string. For purposes of illustration, asingle string is shown in cooperation with the upper surface of theunit. The string 131 is disposed a distance 132 above the upper edge ofthe box. The magnetic lines will then travel upward as shown by thearrow 133 along the string and back down at the outer surface. It isreadily apparent that as the string vibrates, the distance between thestring and the edges of the tray is varied thereby varying thereluctance path. Since the electromotive force is constant, the amountof flux will vary. This change in flux induces an electric current inthe coil 127. Referring particularly to the lip 126a associated with thestring, it is seen that the return path for the flux extends along theentire lip. Thus, by bending the lip towards or away from the string,the reluctance can be incrementally varied. This feature is used tovoice the piano when it is tuned.

The electromagnetic pickups 116-120 are mounted in the housing closelyadjacent to the strings whereby the vibratory motion of the string willresult in a change in the flux linkage on the coils. in practice, it hasbeen found that the spacing of about one-eighth inch from the stringsproduces a suitable output signal. Each of the strings will induce itsown currents and there will be a mixing action on the coil to provide acomplex output signal which is added to the signals from the otherpickup units and applied to the preamplifier. In certain instances aplurality of magnetic pickups may be desired since the spacing betweenthe magnetic pickups and the strings will vary depending upon whetherthey are the bass, midrange or treble strings. It is apparent that thetreble strings will not have as great an amplitude of vibration andthat, therefore, the

ickup unit will be much closer to the strings than is the unit or thebass strings which have a substantial excursion in their vibrations. Inthe present example, the first four units 116, 117, 118, 119 areassociated with one octave each, 12 strings, while the unit isassociated with 16 strings. The outputs of the pickup units are appliedto either directly or through a voicing circuit 26 to the preamplifier27.

Thus, there is provided a piano in which the vibratory motion of thestrings serves to generate electrical signals or oscillations which canbe electronically processed and applied to a speaker. Voicing, tone,special effects, volume, etc., are controlled primarily electrically. Apiano in accordance with the invention will be substantially less costlybecause of the use of electronic circuits.

lclaim:

1. An electromagnetic piano comprising means supporting a plurality ofstrung strings, means including keys and hammers for striking saidstrings to set the same into vibration, a plurality of electromagneticmeans magnetically coupled to selected ones of said strings serving togenerate electrical signals responsive to the vibration of the stringsand having frequencies corresponding to the frequency of vibration ofsaid strings, each of said electromagnetic means comprising a lowreluctance U-shaped tray having a bottom and upstanding walls, a lipformed at the upper end of at least one of said walls and extendingsubstantially parallel to said strings, and elongated permanent magnethaving north and south poles along its edge disposed in said tray withone magnetic pole magnetically coupled to the bottom of the tray and theother pole spaced from and coupled to the upper end of said walls andlip via a gap, a coil coupled to said permanent magnet whereby as thestrings are vibrated they modulate the reluctance across the gap andinduce electrical signals in the associated coil. voicing meanscomprising a resistive-capacitive network coupled to receive the outputof each of said electromagnetic means, means for receiving, processingand amplifying the signals from each of said voicing means. and aspeaker connected to receive said processed and amplified signalsserving to generate sound.

2. A pickup device for stringed instruments comprising an elongatedmagnet having north and south poles along its edge, a coil coupled tosaid permanent magnet, and low reluctance means comprising a U-shapedtray having a bottom and upstanding walls with said magnet disposed insaid tray and having one of said poles magnetically coupled to thebottom of the tray and the other pole spaced from and coupled to theupstanding walls via a gap, a lip formed at the upper end of at leastone of said walls and adapted to extend substantially parallel to saidstrings whereby said lip can be bent to adjust the coupling to selectedstrings to voice the stringed instrument, the reluctance across said gapbeing modulated responsive to vibrations of the strings whereby toinduce an electrical signal in said coil.

